LIPOIC ACID
Alpha-lipoic acid is a nutritional coenzyme that participates
in the energy metabolism of proteins, carbohydrates and fats,
with a particular role in blood glucose disposal. It is also able
to scavenge a number of free radicals.
As both a fat and water-soluble, sulfur-containing
coenzyme, alpha-lipoic acid functions in the body as part
of several multi-enzyme complexes located in the
mitochondria. Alpha-lipoic acid is essential for
metabolizing carbohydrates, proteins, and fats, for the
conversion of their energy into ATP.
Two of these
enzyme complexes, pyruvate dehydrogenase (PDH) and
alpha-ketoglutarate dehydrogenase (KGDH) are part of
the citric acid cycle (Krebs cycle), and as such assume a
central role for general energy production. Another lipoic
acid containing enzyme complex, branched-chain ketoacid
dehydrogenase (BCKADH), is involved in deriving
energy from the branched chain amino acids, leucine,
isoleucine, and valine.
A related metabolic function of alpha-lipoic acid is its role
in blood glucose disposal. This important coenzyme
appears to be necessary for the normal transport of blood
glucose into the cell. This may be explained by its
functions in the glucose-metabolizing enzymes, PDH and
alpha-KGDH, but some researchers suspect a more direct
role in cellular glucose uptake at the cell membrane.
As early as 1959, alpha-lipoic acid was suggested to be an
antioxidant, since it could extend the actions of vitamin C
in guinea pigs, and those of vitamin E in rats. It is only
recently, however, that the specific actions of alpha-lipoic
acid in free radical quenching, metal chelation, and
antioxidant regeneration have been investigated.
Body cells and tissues are threatened continuously by
damage caused by toxic free radicals and reactive oxygen
species (e.g., peroxides) which are produced during
normal oxygen metabolism, and by toxic agents in the
environment. Free radicals, once formed, are capable of
disrupting metabolic function and cell structure. When
this occurs, additional free radicals are produced which, in
turn, can result in more extensive damage to cellular
structure and function.
Alpha-lipoic acid is unique among biological antioxidants,
because it is soluble in both water and lipids. This allows it
to neutralize free radicals just about everywhere in the body,
inside and outside the cells. Due to its unique sulfurcontaining
structure, alpha-lipoic acid can scavenge several
types of free radicals, such as the highly reactive hydroxyl,
and singlet oxygen free radicals.
It is also capable of
suppressing the generation of free radicals in the first place,
since alpha-lipoic acid chelates transition metals, such as iron
and copper. Because alpha-lipoic acid is involved in so
many different antioxidant functions in virtually all body
tissues, it has been called the universal antioxidant.
Besides being a universal free radical scavenger, alphalipoic
acid can also recharge other antioxidant systems
throughout the body. As mentioned earlier, it can extend
the activity of vitamins C and E. In addition, alpha-lipoic
acid can also regenerate glutathione.
